THE AETIFICIAL INCUBATION OP OVA. 43 



of the water will make a difference in the period 

 of incubation equal to something like a half of the 

 entire time — e. g. at 33° or 34°, say a little above 

 freezing, the ova will be above 120 days hatching, 

 whereas at 45° or 46° it will be something like sixty- 

 five or seventy days, and at 50° perhaps from forty 

 to fifty days ; but that which is the longer period 

 in coming forth is often the most healthy and the 

 strongest alevin. But added to this there is a greater 

 evil possibly. "With increased temperature a variety 

 of matters come into existence which are not favour- 

 able to ova, and which a colder temperature has kept 

 in abeyance ; confervoid growths of various kinds 

 begin to vegetate, and insects previously unseen and 

 harmless spring into life and action. The ova turns 

 bad and byssus attacks it with far greater rapidity, 

 spreading under the genial sun as rapidly as fungus 

 does in a cellar. Putridity in every form is en- 

 couraged far more by the warmth than by the cold, 

 as we are all well aware, and putridity of any kind 

 is more or less fatal to ova — of the salmonidee at 

 least. Therefore, it will hardly do to calculate what 

 we can do with so-and-so in the depths of winter, 

 but what we shall be able to. do if the weather 

 should prove open and warm in February and March. 

 In the matter of pisciculture, as in all others, to 



